Understanding and Calculating Work Work - When a force acts on an object and causes it to move through a distance, energy is transferred and work is done.

2 What is work? In science, the word work has a different meaning than you may be familiar with. The scientific definition of work is: using a force to move an object a distance (when both the force and the motion of the object are in the same direction.)

3 Work is done by the mouse

No Work is done! Regardless of the amount of effort or force used, if the rock doesn't move, the person does no work.

Work or Not Work? Is the woman doing work on the box by pushing it across the floor?

Work or Not Work? Is the woman doing work on the backpack by carrying it across the room?

Work or Not Work? Is the woman doing work by lifting the bag off of the floor?

Work or Not Work? Is the woman doing work on the bag of groceries by carrying the bag across the room?

10 Work or Not Work? A scientist delivers a speech to an audience of his peers. A body builder lifts 350 pounds above his head. A mother carries her baby from room to room. A father pushes a baby in a carriage. A woman carries a 20 kg grocery bag to her car?

11 No A scientist delivers a speech to an audience of his peers. No Yes A body builder lifts 350 pounds above his head. Yes No A mother carries her baby from room to room. No Yes A father pushes a baby in a carriage. Yes No A woman carries a 20 km grocery bag to her car? No Work or Not Work?

12 Formula for work Work = Force x Distance The unit of force is Newtons, N The unit of distance is meters The unit of work is Newton-meters One Newton-meter is equal to one joule So, the unit of work is a joule

14 W=FD Work = Force x Distance Calculate: If a man pushes a concrete block 10 meters with a force of 20 N, how much work has he done?

15 W=FD Work = Force x Distance 200 joules Calculate: If a man pushes a concrete block 10 meters with a force of 20 N, how much work has he done? 200 joules (W = 20N x 10m)

16 W=FD Work = Force x Distance Calculate: If a man pushes a concrete block 0 meters with a force of 20 N, how much work has he done?

17 W=FD Work = Force x Distance 0 joules Calculate: If a man pushes a concrete block 0 meters with a force of 20 N, how much work has he done? 0 joules (W = 20N x 0m) No distance, no work!

How much works is being done? The barbell’s weight (a force) is 40 Newtons and is lifted 1 meter. The force needed to lift an object is equal to the gravitational force on the object-in other words the objects weight

How much work is being done? Now the barbell’s weight is 80 Newtons and is lifted 1 meter. Increasing Force while leaving the distance constant causes more work.

How much works is being done? Now the barbell’s weight is 40 Newtons and is lifted 2 meter. Increasing distance while leaving the force constant causes more work.